Principal Sharon Sopher wrote a three-page letter to families on September 11, describing the plebiscite as a “relatively unique event in our democratic history” and encouraging the school community to participate.

“It seems unlikely that any similar opportunity will arise in the future to express an opinion on what is a fundamental building block of our society, so we must act now,” she wrote in the letter. 

“There is a clear and acknowledged link between changing the definition of marriage … and religious freedom. We are, respectfully, asking all those associated with the school community to participate and vote ‘no’ in the survey. We ask this in love, and out of love ... we will certainly be praying and trust that you will join us.”

Ms Sopher declined to answer the Newcastle Herald’s questions about the school’s policy regarding staff and students who supported, were in, or had parents from same-sex relationships; and whether and in what context staff had discussed the issue of same-sex marriage and the plebiscite with students.

“Our school is concerned … about our ongoing ability to continue to teach and model our [Christian] views on marriage and family,” Ms Sopher told the Herald. “Despite requests being made to the government to release proposed legislation prior to the commencement of the survey, this has not occurred and there is simply no certainty around what legislation may be proposed.

“In other words, a ‘yes’ vote is like signing a blank cheque to the Parliament to proceed with changes without having received any details of what, if any, protections for religious freedom might be provided. We have grave doubts … that enough ‘careful attention’ is being given to the flow on effects.”

The letter, which quoted the Bible, said the question about changing the law reflected a worldview that was “dramatically different to the Biblical worldview to which we hold as a Christian school” and implied an understanding of “marriage as merely a legal construct”.

It said the school’s views were not expected “to come as any surprise”.

The Independent Education Union said legislation should consider the wellbeing of same-sex couples and their children and "the needs and teachings of faith-based communities in respect of their understanding of the sacramental marriage”. A spokesman said any school wanting to communicate with parents about the plebiscite should not “use students as messengers”.